For a lot of growing Australian businesses, pay-as-you-go (PAYG) SIP is a sensible place to start. After all, they pay only for the calls they make. That tends to suit teams whose calling still changes month to month. Once their call volume settles at a high, steady level, an unlimited plan may work out cheaper, but figuring out where that point sits is easier than it sounds.
What is a PAYG SIP trunk?
A PAYG SIP trunk is a business phone service delivered over your internet connection, where you pay a fee for each call channel plus a separate charge for each call made. Costs rise and fall with how much your team actually calls, which makes PAYG a common choice for businesses with moderate or unpredictable call volumes.
SIP stands for Session Initiation Protocol, the standard that lets your phone system make calls over a data connection instead of copper lines. The “trunk” is the link between your phone system (an IP PBX or PABX, in your office or in the cloud) and the carrier.
Each trunk is made up of channels, and one channel carries one call at a time, inbound or outbound. With five channels, the sixth caller gets a busy tone or voicemail.
How PAYG pricing adds up
Your bill has two parts: the channel fees, which stay the same each month, and the call charges, which move with usage.
At the time of writing, Com2’s PAYG SIP trunk rates are at $7.50 per channel, 10 cents per local or national call, and 16 cents per minute to mobiles.
Local and national calls are a flat amount, no matter how long you talk. Mobile calls are charged by the minute, so mobile minutes are usually the part of the bill that moves most, especially for trades, real estate and sales teams who spend the day ringing clients’ mobiles.
In most setups, receiving calls on a standard local number does not cost anything per call. Inbound 1300 and 1800 numbers are different, as they carry their own charges.
Why PAYG suits a business that’s still growing
Growth rarely happens in a straight line. You hire two people in March, lose a big client in June, then open a second office. PAYG handles that kind of movement well.
- Channels can go up or down. At Com2, more channels can often be added on the same day, so you are not stuck waiting weeks when the phones get busier.
- No lock-in contract. Com2 does not put contracts on its PAYG SIP. If your needs change, you are free to move to a different plan or provider without a break fee.
- Quiet months cost less. Seasonal businesses, such as tourism operators or accountants outside tax time, are not paying for call capacity they are not using.
- Your numbers can grow with you. You can port your existing numbers across, add local numbers from another state (02, 03, 07 or 08) when you open a new site, or bring in 1300 numbers for a national presence.
Pro Tip: Growth often shows up in your channels before it shows up in your bill. If staff are hearing that customers got a busy tone at 10 am on a Monday, you probably need another channel, not a different plan.
When does PAYG stop being the cheaper option?
PAYG usually stops being the cheaper option when your monthly call charges regularly exceed the gap between PAYG and an unlimited plan for the same number of channels. For most businesses, mobile minutes drive that tipping point, because they are billed per minute while local and national calls are usually charged per call.
Here is a simple way to test it, using the rates above.
Say you run a 12-person office with four channels. In a typical month, the team makes 500 local and national calls and spends 800 minutes on mobile calls.
- Channels: 4 x $7.50 = $30
- Local and national: 500 x $0.10 = $50
- Mobiles: 800 x $0.16 = $128
- Total: about $208 a month
Now ask for an unlimited quote on four channels. Com2 prices its unlimited plans based on each customer’s needs, so there is no single figure to compare against. If the quote comes in well under $208 and your usage is fairly stable, unlimited is likely the better deal. If your mobile minutes swing between 300 in a quiet month and 1,500 in a busy one, PAYG may still come out ahead across the year.
| Plan type | How you pay | Tends to suit | Watch out for |
| PAYG | Monthly fee per channel, plus a charge per call or per minute | Moderate or changing call volumes, seasonal businesses, new sites | Busy mobile-heavy months, and higher exposure if your system is hacked |
| Unlimited | Higher fixed monthly fee per channel, with local, national and mobile calls included | High and steady outbound calling, mobile-heavy teams, budgets that need a set figure | Fair use policies, and paying the same in quiet months |
| Mixed approach | Some channels on unlimited, extra capacity on PAYG (availability varies by provider) | Businesses with a steady base load plus busy peaks | More moving parts to track on the bill |
The mistake to avoid is running this sum once and forgetting about it. Use your average from the last three months and your busiest month, then revisit it every six months or so. A business that was a clear PAYG fit last year can quietly become an unlimited fit after a round of hiring.
How many SIP channels does a growing business need?
The number of SIP channels a business needs depends on the most calls it handles at the same time during its busiest period, not on its headcount. A 20-person office where staff rarely overlap on calls might get by with five or six channels, while a small sales team that calls all day could need one per person.
The easiest way to find your number is to look at your phone system’s call reports for your busiest hour of the week. Many modern systems, including 3CX, can show peak concurrent calls. Take that peak and add one or two channels as a buffer.
No reports to look at? Ask the front desk when the phones feel busiest and start from there. On PAYG, getting it slightly wrong early on is easy to fix.
What to check before you switch
Like all SIP trunks, a PAYG service relies on the rest of your setup being ready. These are the checks worth doing first.
Your internet connection
Each call typically uses around 100 kbps in each direction on the common G.711 codec, so ten calls at once need roughly 1 Mbps of upload and download set aside for voice. That is modest, but upload speed is often the weak point on standard NBN plans, and voice competes with video meetings and cloud backups.
Ask whether your router supports Quality of Service (QoS), which puts voice traffic at the front of the queue. If your phones are critical to the business, a business NBN plan with a mobile backup connection is worth considering.
Your phone system
Most modern phone systems support SIP out of the box. Older systems from brands like NEC, Panasonic, Avaya and Mitel may need a SIP licence or a gateway. It is usually possible to connect an existing PABX to SIP without replacing the whole system, which can help keep the cost of switching down.
Security and spending limits
This one matters more on PAYG than on any other plan. Toll fraud happens when someone gains access to a poorly secured phone system and uses it to make expensive international calls, often overnight or on a weekend. On a pay-as-you-go plan, those calls end up on your bill.
Warning: Before you go live, ask your provider about international call barring, spend alerts and call limits. Make sure your phone system uses strong passwords and sits behind a properly configured firewall.
Emergency calls and power
A VoIP phone needs power and internet to call anyone, including Triple Zero (000). Keep a charged mobile on site, and make sure your provider has the correct street address registered against each number, so emergency services are sent to the right place.
So, is a PAYG SIP trunk worth it for your business?
For most growing businesses, PAYG is worth it while call volumes are still changing, because you only pay for what you use and can adjust as you go. The case for switching to unlimited gets stronger once your mobile minutes are high and steady.
To find out where you sit, pull your last three months of call records and note your peak concurrent calls, local and national call count, and mobile minutes. Cost that on PAYG using the method above, then get an unlimited quote for the same channels. If the gap is small or your numbers still bounce around, staying on PAYG keeps your options open.
Our expert team at Com2 can look over the numbers with you and suggest a setup that fits your phone system. Contact us today to get started.